Radioiodine in the atmosphere after the Fukushima Dai-ichi nuclear accident

About 160 PBq of 131I was released into the atmosphere during the accident at the Fukushima Dai-ichi Nuclear Power Plant. The chemistry of radioiodine is complicated, and it can be released in several different forms. In addition, the different physical forms, like molecular iodine, aerosol-form iodine, or organic iodine, would have all behaved differently once in the atmosphere, and would have been removed at different rates. These releases were detected by monitoring stations throughout Japan, and from these measurements, key insights can be made about the different chemical forms that were released, as well as the persistence of each in the environment. [Display omitted] •Measurements of airborne iodine emitted from the Fukushima accident were examined.•Atmospheric ratios of molecular, organic, and aerosol form iodine were inferred.•Major emissions were likely mostly vapour-form iodine.•Post-accident background near the Fukushima Dai-ichi site was mostly in aerosol form.•Far-field iodine, away from accident site, was likely primarily in organic form.